Is whitening your teeth hygenic or cosmetic? What if your teeth are gross looking? Are brown teeth holy?

“Cleanliness is next to Godliness.”
Brushing teeth is hygiene/medical.
Whitening teeth is cosmetic.
But your teeth can be whitened accidentally/secondarily while your primary motive is medical (to prevent decay).

Are there any other moronic attempts to confound hygiene and grooming with cosmetics?

Probably.

No, certainly.

I leave you to your misery.

Cleanliness is next to Godliness.”

It’s not scriptural at all but comes from the heretic, John Calvin, who’s extremism caused him to believe in such false notions.  Calvinism is the precursor to the excesses of capitalism (time is money), and the modern “rewarder God” theory which says that you’ll be blessed economically if God loves you

This must be the rule of double effect  of white teeth in action

  Perhaps we can find the exact citation for this in the Summa.

I work out at the gym not only to feel better and be more healthy, and more strong, but also so I don't get fat and flabby and weak and unmasculine ... so as to embarrass my wife (hey, look at that fat guy she's with).  I do not work out to catch the eye of anyone but my wife.  And women who use makeup with the same set of intentions ... to look more feminine and to please their husband and not to embarrass them, etc. ... they likewise commit no sin.  Now, if they were doing it to get "checked out" by other men, then that's sinful, or if there are degrees of vanity, or if they are excessive in its use ... those are different stories.

I don't think the term "Cleanliness is next to Godliness" is scriptural- where does it come from?
It always reminds me of the contradiction of St John the Baptist who lived in the desert, wore skins and ate locusts and wild honey...He certainly was the greatest among men and closest to God, but probably not too clean. What say you?

Goodness gracious! He was in and out of the Jordan on a regular basis. How dare you disparage St John the Baptist!
  :heretic:   

If women who wear subtle makeup up sin, so also do men who wear contacts. They sin by their vanity.

I had to laugh when I read this thread topic. Here's a random personal anecdote to go along with your (sarcastic) premise:
.
I've worn glasses since age 3, but only wore contacts for a few years in my early 20s. At that time, I was helping a small religious group by assisting with the music at some of their retreats. They normally only saw me with contacts, but one evening at a practice, I was wearing my glasses. One of the sisters asked about them and I started to explain why I wasn't wearing contacts at that time, but without letting me finish the sentence, she ended it for me, with "vanity". The thought hadn't crossed my mind as I was only concerned with my eyes getting too dry (per doctor recommendation), but she was probably correct at least to some extent. I certainly (at least at that time) had no practical reason for wearing contacts, it was one of several things I did around that age solely because I thought it would improve my appearance. I completely stopped wearing contacts later not through some virtuous motive (despite Sister's not-so-subtle opinion), but because the arrival of small children and odd sleeping patterns meant I was waking up with contacts stuck to my eyeballs way too often.